Radio circuit



Dec. 8, 1931. w, SCHEPPMANN 1,834-,975

RADIO CIRGUIT Filed Jan. 27. 1927 Patented Dec. 8, 1931 i 1 ..j/UNITED s'rn'resI PATENT oFrics Application filed January 27; 1927, Serial No. 164,020, and n'Germany February 3, 1926.

I This invention relatesvbroadly to the art tially Wound Windings to have the same magoffradio engineering and more particularly nitude i. e. the same number of amperes in to all case-s Where a4 compensating circuit arorder to neutralize their actions upon a. currangement is required such asis in use for rent sensitive device e. g. the armature of the the suppression of an interfering-signal in relay. lVhen dealing 'With alternating 01' u the reception of radio.signals,or for'any oscillating eurrents in compensating eircuits other circuit systems in Which a differential a further condition is to be fulfilled to satisfy or compensating action of currents of a distothis end in that, to obtain complete neutinct frequency is totake place. tralizing effect, the two compensating curvIn carrying out my invention I provide a rents besides having equal amplitudes, must 60 circuit arrangement embodying two circuit always have a phase difference of 180. paths in order to transmit currents from an There are known means to change the phase input circuit to an output ,circuit and I; renof radio currents and so satisfy this condition, der these circuit paths transparent to the but these means are troublesome and in most currents of the-frequency Which is to be neucases inaccurate and they make necessary rctralized in the associated output circuit prefadj ustments when passing from one Working erably by introducing into one of these cir- Wave length to another' one. This method, euit paths an acceptor circuit tuned to therefore, can not be used in radio circuits, such particular frequency and therefore prein'which a constant change of frequency or A0 senting zero impedance for. same,` so that tuning is required. It is, therefore, a special 7" currents of this frequency Will be delivered advantage of the novel circuit arrangement at substantially equal magnitude to the .outin accordance With my invention, that phase put circuit associated equally \vith both ,ciradjustments may be entirely dispensed with. cuit paths. By virtue of this relation of the For, the acceptor circuit introduced into one circuit paths to the associated output circuit of the 'compensating circuit paths presents 75 being so arranged as to have thevcurrents in Zero impedance to the current of its resonant the latter oppose each other the resulting effrequency, it being therefore not necessary feet in the associated circuit forucnrrents of to introduce a phase shifting device into the such frequency Will be Zero. It follows, other circuit path for balancing purposes.

I therefore, that for all currents of a frequency The currents have only to be adjusted to equal 30 other than that to Which the mentioned acamplitudes as is the case when dealing With cep'tor circuitis tuned to, thev latter presents direct current systems. a-n effect equivalent to that of a large imlVIy invention finds particular,application pedance .and consequently prevents currents in radio receiving systems, Where it is desired of all frequencies other than the resonant freto suppress one or more undesired interferquency of the acceptor circuit to pass thru ing signal frequencies, but it may be of use only one of said circuit paths. The neutraltoo in transmitting systems, e. g. for sup- .izing effect of these frequencies in the' assopressing undesired harmonics and thus preciated common circuit is therefore rendered venting them from being radiated and causinefl'ective, only the resonant frequencyV of ing interference in receivers. It may be emthe aeeeptor circuit being substantially neuployed too for the suppression of the carrier tralized in the associated output circuit. frequency in so-called single side band Wire- The circuit arrangement according to my less telephone transmission systems With carinvention presents special advantages, more rier suppr'ession. Another application of fully hercinafter explained. V I the circuit arrangement according to my iu- When effecting a compensating or neuvention is to serve in a Wave meter acting by tralizing action With direct currents, such as a so-calle(l null methodas Will be hereinis the case e. g. With diferentially Wound reafter more fully set fert-h. lays and the like it is only necessary for the My invention Will be better understood by tWo currents flowingthru the two diferenthe following detailed description taken With reference to the accompanying drawings of which Fig. 1 is a wiring diagram showing the general principle of the subject matter of the invention, and of which,

Fig.. 2 is a schematic diagram showing a radio receiving systemintended to eliminate an interfering signal and having -forthis purpose the circuit arrangementfof my invention incorporated in it,l and W Fig. 3 shows another embodiment of my invention in a transinitting system with the-circuit arrangement of my invention associated therewith for the suppression of the carrierV frequency for single side-.band telephone systems with carrier suppression.V i

- c Referring'more .particularlyto the diag'ra-In i-l'lustratedin Fig. 1, 8 and 9 are the input and 10 and 11 the output Lterminals-of a radio circuit system of any kind. in Vwhich it is desired to-&prevent currents of a distinct frequency to be transmitted from the input circuit at S, 9 to the output circuit at: 10, '11. For. this purpose two compensating circuit paths Vare-.provided each containing a sel-finductance l and 2 Vrespectively ,Sym'metrical'ly arranged -which are-,coupled in opposite relationship ,by coi'ls and 4 respectively to ythe .associated output circuit vConnected at the output terminals 10 fand 11 so as to produce opposite effect-s'tlierein. Into one of thecurrent paths there Vis introduced an'accepto'r circuit consisting ofa self-indu'ction coil' 5 in series with a capacity 6 'and .tuned 'to the frequency of the current which is -to-besuppressed. VAs this acceptor circuit has for" the currents of its resonant frequency an effect equivalent to Zero impedance, the ba-la-ncing conditions for such current are maintained and the neutralizing effect -in the associated circuit rendered effective. Theicircuitpath containing the acceptor circuit 5, `6 presents to the 'current of -its reson'ant frequency a short-circuit vWhereas for currents 'of differ- Aing frequencies -the effect -of it is .that of a It is' thus possible to obtain a complete neuti'ializing* effect with respect to Vcurrents of the undesired frequency, all other frequencies being transferred int-o the associated ciri cuit. As the acceptor circuit-'5, 6 presents only ohmic resistance to its resonant fre-` quency, only-a balancing by an ohmic resistance 7 is necessary such as is the case With direct current systems and laboriousphaseshifting operations are avoided.

Referring to Fig. 2 of the drawings the novel feature of my invention is shown incorporated ina radio receiving system, in which an interfering signal is to be prevented from entering the receiver, such as is the case with radio plants on ships, Where sending and receiving aerials'are necessarily arranged close together and where for simultaneous transmitting and receiving the receiver must be protected against thestrong interfering signals of the transmitter. The circuit arrangement 'forming the subject matter of my `invention may be lof :use .too When receiv- -ingdistant bro-'adcasting stations in the neighborhood of a local station and in other like cas'es. The wiring diagram represented by Figu're 2 only difers from Fig'ure 1.in that 4at thelbranching l:points aV and: Z) a receiving afntenna-earth system 12, 13 is Connected forming thus an'input circuit. All other ref-' erenc'echaracters similar to that used in Figure 1 refer to eopiivalentelements.V At the output 'terminals 10, 11 a well-known amplifying or detecting system for thesignal 'frequency may be cOnneCted, e. g. there may be associated: an oscillatory circuit tuned to .the signal "frequency Which influences the grid of a =thre'e-electrode discharge device actingas detector or amplifier in' combination With further devices'to obtain an amplfified signal which is finallyv supplied to a translating' device.H But asthis is out of the scope-of the present invention Va further description maybe dispensed with.

VVhen'em'ploying a systemV according to Figlure 2- also'simulta'neous transmitting and receiving/with, the :same aerial may be carried out, i t being only necessary to connect the transmitting apparatus outside'the compensating circuit i. e. outside the points a and If "two or more undesired frequencies are to be "suppressed, the compensa'ting -circuit 4arramgemen't'just described may be emp'l'oyed in successive stages.v In thiscas'e, instead of a receiver, there is to bel Connected at the output terminals 10 and 11 a second cvompensating arrangement analogous to the first oneand having its individual acceptor circuit tuned to 'another frequency' Which is .to be 'prevented from being transmittedto the receiver.

When carrying into practice a circuit` arrangement in 'accordance with my invention the 'coils 1," 2, 3 and 4 are preferably to be constructed in the form of a difi'erential transformer. The coi'ls 3 and 4 may also] be dispensed Iwith andthe output or receiving circuit may then be Connected at the points c Vandwjclinstead of atithe. terminals 10 and 11.v 'The'latte'r method is equivalent to a conduotve copling ofthe' outputcircuit in'- 'L Ilent elements. The circuit shown with :in

stead of an Vinductive one as is the case in Figs. 1 and 2. The effect is in both cases the samo.

Beferring to Fig. 3 of the drawings a 'transmitting wiring diagram is shown intended for the suppression o-f the carrier frequencv in radio telephony and having to this enoL the circuit arrangement of my invention incorporated in it. It has already been proposed when transmitting modulated radio frequency currents particularly in carrier telephony with or without a wire in which besides the carrier frequency there' exist two frequency bands more or less large and lving symmetrically With respect to the carrier frequency, to prevent the` latter from being transmitted and thus transmit only the two or only one of the side-frequency bands. This makes it necessary to add at the receiving end the carrier frequency afresh by means of a small loca'l oscillator in order to obtain an intelligible signal. Que advantage of this method consists in that by .the suppression of the carrier frequency its energy is applied on the side bands, and the secrecy of the signal. with respect to unauthorized persons is increased it being only possible to an intelligible signal for the person who is able to add the right carrier frequency. A further advantage when working with one side band' only is the possibility of more stations being allowed to work within one given range of wave 'lengths, and especially when workinga on longer waves, of the farthest side frequencies not being chopped off in the sharply tune/d receiver. By employing a circuit arrang'c nent as proposed by my invention the carrier frequency may besuppressed in an effective and very easy Way. Reference characters in Fini. 23 same as those in Figs. 1 and 2 refer to cauiv antenna-earth system compri sin o; the antenr:: 14', a loading coil 15, the diferential coi 3 and 4 in accordance with the inventi-fr and the earth connection 16, the antenna circuit forming' thus the output system of the compensating' circuit arranc'emcnt. The input circuit is an intermediate circuit consisting of a capacity 17 and a coil 18 coupled to an oscillation `generation? apparatns 9.53 of any kind Connected to the terminal of the coupling coil 19. 20 is a inafrnetic amnli'lier with its higli-frerpiencyT win/dinu' 21 insertei'l into the input circuit 17. 18. The conzr-:illinggI winding` 22 supplied by a local direct eurrent source 23 in series with a mici-milione 24: to modulate the radio currents in accordance with speech oscillations.

The acceptor circuit 5.y 6 inthis case is tuned to the frequency of the carrier currents, other operating details being sul'istantially equal to those underlying the operation according to Figures 1 and 2.

In order to render the neutralizing` arrangemcnt very selective the damping factor of the acceptor circuit is to be given a value as low as possible which may be accomplished by making the self-iiuluctance quite large and by making` the capacity 6 small.

Another application of the compensating circuit arrangcniont of my invention is that of scrving' as a wave nictcr will be described more fully hercinafter it being; suflicient for simplici salie to refer to Fini. 1. The method ordinarily used in wireless engineering for indieating` or measuring Wave lengths is b d on the well-known resonance phenonieua in osciilatinfjr current circuits. In order to iiulicate the wave length of an oscillation prmluced by a generator or transinitted by an anteuna, an oscillatory circuit having as 'low a damping` coeiiicient as possible is coupled lo-'iselv to the generator or to the antenna respc veli. lf the natural frequency of this oscillatoriv measuring circuit rendercd resonant to the frequency to be measured by means of adjustablo tuning;I means, a maximum of current flow is established in it. Vv'hen obscrving this mm:- imum current -by means of a suit-able voltmeter or :nnpere-nieter the wave length may be calculated aiulif the measuring circuit is calihrated in advance the wave length may bo read Li. tantly. For an aceurate determination of the wavc llength according to this resonanoe principle which as for accuracy depends upon the sharpncss of the pcat. of the. rcsenance curve, it is necessary for the measu *i* circuit to have ar low a dan'ipmg fa-tor as possible and to be in loose couplinn' with the circuit whose current is to be measured. These conditions, in practice, may only be fuliillcd to a certain extent.

In emploijiing the circuit arrangement of my inven tion l may obviate these inronvenicnees by connecting` the circuit containing the current whose frequency is to be determined the input terminals 8, 9 of the circuit arrangjcment and by connecting at the output terminal and 11 a current indicating device M. Then I change the natural frequency of the acceptor circuit 5, 6 gradually by making the Variable condenser G and tapping the inductancc at several points such as shown at 5, till the indicati device at 10, 11 does not show any reading' and remains at zero. As will bo readily seen the natural frequency of the acceptor circuit 5, G is then equal to the frequency of the curre .t to be measured. The condenser may be calibrated directly in wave lengiths so that a direct reading' may be carried out. As is seen this method is a socalled null7 method possessinp; as every null method the advantage of high sensitiveness, it being possible to cinploy very highly sensitive indicating instruments. The resistance 7 has not to be adjusted afresh for each new position of the condenser, but is only to be given several constant values corbe rendered close at will. 1 The indicating circuitis to be protected against being directly 'influenced byV the generator circuit, e. g. by

shielding it electrostatically.

As the current in the indicating circuit assumes a considerable value by the slightest detuning of the frequency to be indicated with respect to the frequency to which the acceptor circuit'is tuned, the arrangement may serve as a control device of a VWave length Which is to be held at a constant value, e. g. that of the Wave length transmittecl by an aerial in a transmi-tting station.

`According to another feature of my invention it cnables the determination and measuring ofhigher harmonics in Wireless circuits to be readily carried out. The known radio frequency Vgenerating systems such as vacuum tube transmitters, Poulsenarc transinitter or machine transmitters produce besides the fundamental signaling frequency other frequencies being more or less distant from the signaling frequency and having considerably smaller magnitude. These frequencies are known as higher vharmonics and side frequencies. They. are in most cases very un desired and present difficulties in the determination of their magnitude and wave length. When using an ordinary Wavemeter in theneighborhood of a strong transmitter, it would absorb such a quantity of current of the fundamental frequency thatrit would be impossible to discern the weaker higher harmonics and a reso- -nance curve plotted in accordance withreadings would only show the conditions of the fundamental and Would not show the conside'rably Weaker higher harmonics. Only by very accuratelymeasuring and plotting the curve would the higher harmonics be indicated in the resona-nce by smallelevations. But in this case, too, there could not be obt-ained a direct and eXact measuring of theirv magnitude the influence of thefundamental being so strong as to allow only a rough appreciation of their relative strength. When employing an arrangement according to my invention the disturbing fundamental frequency may VbeV neutralized and prevented from pass'ing into the wavemeter, Whereby the measuringof the harmonics in the latter may now be easily carried out. Referring to the general wiring diagram of Fig. 1, the circuit containingV the higher harmonics to be Vmeasured isconnectedat the input terminals 8 and 9., whereas the output terminals 10, 11 lead to a normalwavemeter. The rejector circuit 5,

6 is tuned to the fundamental frequency Which is accordingly neutralized in the Wavemeter circuit, thereby only the higher harmonics to be allowed to pass into the Wavemeter circuit where they can now easily be indicated.

The principle of operation of my invention has been already discussed, but it might be v pointed out that the broad operating-princirents of undesired frequencies may be carricd out entirely independent of phase adjust-ments. A V

' VVhile I, have described my invention in certain specific embodiments, itwill be understood that I. intend no limitations other than are imposed by the scope of the appended claims. 1. Y

Having thus described my invention, what I claim and desire to Secure-by Letters Patent of the United States is:

l. The combination in av radio circuit arrangement of the character described of an output circuit, an input circuit having two circuit paths that are in equal and opposite coupling relationship to said output circuit to produce oppositc effects therein, only one of said circuits being a tuned circuit and comprising an acceptor circuit introduced into one of said circuit paths and tuned to the .frequency of the current to be neutralized in the output circuit.

2. The combination in a 'radio circuit ar- 'angement of-the character' described of an output circuit, an input circuit having two circuit paths that are in equal and opposite coupling relationship to the output circuit to produce opposit-e effects therein, an acceptor circuit introduced into one of said circuit paths and tuned to the frequency of the current to be neutralized in the output circuit, and an ohmic resistance-equivalent to the resistance causedby losses of said acceptorcircuit introduced into the other one of said circuit paths. i

3. The combination in a radio circuit arrangement of the character described of an output circuit, an input circuit having' two circuit paths that are in equal and opposite coupling relationship to the output circuit to produce opposite effects therein, only one of said circuits being a tuned circuit and comprising-an acceptor circuit having a comparatively small capacity ,and a relatively large inductance introduced into one of said circuit paths and tunedrtothe frequency of the current it is desired to be neutralized in the output circuit.

4. The Conibination in a radio Circuit arrangement of the character described of an output Circuit, an input Circuit having two circuit paths that are in equal and opposite coupling relationsliip to said output circuit 'to produce opposite effects therein, an acceptor Circuit having a comparatively small capacity and a relatively large inductance introduced into one of said circuit paths and tuned to the frequency of the current it is desired to be neutralized in the output circuit, and an ohmic resistance equivalent to the resistance caused by losses of said aC- ceptor circuit introduced into the other of said circuit paths.

5. The Combination in a radio circuit arrangeinent of the character described of an output circuit having an induction coil therein, aii input circuit having two circuit paths containing` syininetrically arranged coupling coils Coupled oppositely to said induction coil to produce opposite effects in the output Circuit, an acceptor circuit introduced into One of said circuit paths and tuned to the frequency of the current to be neutralized in the output circuit, and an ohiniC resistance equivalent to the resistance caused by losses of said acceptor circuit introduced into the other one of said circuit paths.

6. The combination in a radio circuit arrangeineiit of the character described of an inputcircuit having two circuit paths, an output circuit coiuiected at points of equal potential of said circuit paths to have produced opposite effects in it by current flowingl thru said circuit paths, an acceptor Cii'- cuit introduced into one of said circuit paths and tuned to the frequency of the current to be neutralized in the output circuit, and an ohmic resistance equivalent to the resistance caused by losses of said acceptor circuit introduced into the otlier one of said circuit paths.

'.7. The coinbination in a radio telephone transmission system with carrier supprcssion of an antenna circuit, an input circuit that is supplied by high-frequency oscillations inodulated in accordance with speech currents to be transmitted and having two Circuit paths in equal and opposite coupling relationship to said antciina circuit to produce opposite effects therein, an acceptor Circuit introduced into one of said circuit paths and tuned to the carrier frequency employed for the transi'nission, and an ohinic resistance equivalent to the resistance caused by losses of said acceptor circuit introduccd into the other one of sai d circuit paths.

8. The coinbination in an electric carrier suppression cominunicati on system of a transinitting circuit, an input circuit, means for applying carrier current oscillations inodulated in accordance with signal currents to be transmitted to said input circuit, two Circuit paths Connected to said input circuit and coupled in equal and opposite relationship to said transmitting circuit, to produce opposite efi'ects therein and an acceptor circuit Connected in the first of said circuit paths and tuned to the frequency of said carrier currents employed for the transmission.

V9. The combination in an electric carrier suppression communication system of a transinitting circuit, an input circuit means for applying carrier current oscillations modulated in accordance with signal currents to be transmitted to said input Circuit, two circuit paths Connected to said input circuit and coupled in equal and opposite relationship t'o said transmitting circuit to produce opposite effects therein, an acceptor circuit connected in the first of said circuit paths and tuned to the frequency of said carrier currents einployed. for the transinission, and an ohmic resistance equivalent to the resistance of said acceptor circuit Connected into the other one of said circuit paths.

10. The combination with a carrier suppression communication system of the character described .of a transmitting circuit, an input circuit, means for applying` carrier current niodulated in accordance with signal currents to be transmittcd to said input Circuit, two circuit paths Connected to said input circuit and couplcd in equal and opposite relationship to said transmitting circuit, such trausmission system being Connected at points of equal potential in said circuit paths to have produced opposite effects in it by currents flowing through said circuit paths, and

an acceptor circuiticonnected in one of said circuit paths and tuncd to the carrier frequeiicy employcd for the transinission.

` 11.V The Combination with a carrier sup- 'pression communication system of the charvacter described, of a transinitting circuit, an

input circuit, means for applying carrier currents'inodulated in accordance with signal lcurrents'to be transmitted to said input circuit, two circuit paths, said transmission systein being Connected at points of equal potential in said circuit paths whereby opposite veffects are produced in sald system by currents flowing through said circuit path, an acceptor circuit Connected in one of said circuit paths and tuned to the carrier frequency cmployed for the tranf-:inission and an olimic resistance equivalent to the resistance caused' by loss of such acccptor circuit Connected in the other one of said circuit paths.

12. Means for cliininating undesired frequencies iii a radio transmitting system Coinprising` a source of modulated currents, an acceptor circuit Connected to said source which is resonant to the frequency of said undesired frequency to be eliminated, a secoiid circuit Connected to said source, an antenna Circuit and means for iinpressing upon the antenna el'ectroinotive forces deri-ved froinwhoth of said circuits toproduce opposite ,effects therein. A

18.V Means for 'eliminating disturbing ef- 1 fects in a radio transmitt-ing,` system comprising a source of modulated carrier currents, an acceptor circuit connectedtosaid source Which Y is resonant to the frequency of the disturbing effect to he eiiminated, a second circuit con- -wv nected to said source, the resistance of the acceptor. circuit being substantially vequal to theresistance of the second circuit, an antenna circuit and means for impressing upon the antenna electroinotive forces derived from 1.5 both of said circuits to produce opposite ef,-

f'ects therein. i i

14. A transinittingsystem for radio signals comprising a. source of modulated carrier currents, and means for deriving from said source and impressing upon atransmitting circuit two radio frequency electromotive forcesvof equal intensity and opposite sign produced by undesired Waves of definitefrequency in said modulatedcurrents, said means 59;, being;` arrang'cdto impress luponthe transmitting circuit tWo eiectromotive forces produce;L in said source by' desired signaling currents and Which Will addin the transmitting circuit. i w 'gu '15. Means for 4eliminating` undesired frequencies in a radio transmitting system comprising a source of modulated currents, an ac- Vceptor circuit Connected to said source Which is resonant to the undesired frequency to be eiiminated, a second circuit Connected to said source Which co-mprises pure ohmic resistance, an antenna circuit and means for impressing 'upon the antenna electromotive forces derived from bothof said circuits to produce opposite effects therein. V A16. Means for eliminating undesired fre- .qnoncies in a radiotransmitting system comvprising a source of modulated carrier ourrent-s, an acceptor circuit Connected to said source Which is resonantto the undesired frequency to he eliminated, a second circuit Which comprises pure ohmiclresistance connectedto said source, the resistance of the accep-tor circuit being,I substantially equal to 50 the resistance of the second circuit, an antenna circuit and means for impressing upon .the antenna electromotive forces derived from both of said circuits.

In testimony Whereof I have affixed my signature.

WILHELM soi-IEBPMANN. 

